Implement Fallback for microsoft's terminals. (#138)

I finally got access to a computer using the Microsoft's Windows OS.
That's the opportunity to find and mitigate all the problems
encountered. This patch:

1. Introduce an option and a C++ definition to enable fallback for
   Microsoft's terminal emulators. This allows me to see/test the
   Microsoft output from Linux. This also allows Windows users to remove
   the fallback and target non Microsoft terminals on Windows if needed.

2. Microsoft's terminal suffer from a race condition bug when reporting
   the cursor position:
   https://github.com/microsoft/terminal/pull/7583.
   The mitigation is not to ask for the cursor position in fullscreen
   mode where it isn't really needed and request it less often.
   This fixes: https://github.com/ArthurSonzogni/FTXUI/issues/136

3. Microsoft's terminal do not handle properly hidding the cursor. Instead
   the character under the cursor is hidden, which is a big problem. As
   a result, we don't enable setting the cursor to the best position for
   [input method editors](https://en.wikipedia.org/wiki/Input_method),
   It will be displayed at the bottom right corner.
   See:
   - https://github.com/microsoft/terminal/issues/1203
   - https://github.com/microsoft/terminal/issues/3093

4. Microsoft's terminals do not provide a way to query if they support
   colors. As a fallback, assume true colors is supported.
   See issue:
   - https://github.com/microsoft/terminal/issues/1040
   This mitigates:
   - https://github.com/ArthurSonzogni/FTXUI/issues/135

5. The "cmd" on Windows do not properly report its dimension. Powershell
   works correctly. As a fallback, use a 80x80 size instead of 0x0.

6. There are several dom elements and component displayed incorrectly,
   because the font used is missing several unicode glyph. Use
   alternatives or less detailled one as a fallback.

CMakeLists.txt

@@ -13,6 +13,17 @@ option(FTXUI_BUILD_TESTS "Set to ON to build tests" OFF)
 option(FTXUI_BUILD_TESTS_FUZZER "Set to ON to enable fuzzing" OFF)
 option(FTXUI_ENABLE_INSTALL "Generate the install target" ON)
 
+set(FTXUI_MICROSOFT_TERMINAL_FALLBACK_HELP_TEXT "On windows, assume the \
+terminal used will be one of Microsoft and use a set of reasonnable fallback \
+to counteract its implementations problems.")
+if (WIN32)
+  option(FTXUI_MICROSOFT_TERMINAL_FALLBACK
+    ${FTXUI_MICROSOFT_TERMINAL_FALLBACK_HELP_TEXT} ON)
+else()
+  option(FTXUI_MICROSOFT_TERMINAL_FALLBACK
+    ${FTXUI_MICROSOFT_TERMINAL_FALLBACK_HELP_TEXT} OFF)
+endif()
+
 add_library(screen STATIC
   src/ftxui/screen/box.cpp
   src/ftxui/screen/color.cpp

cmake/ftxui_set_options.cmake

@@ -36,6 +36,11 @@ function(ftxui_set_options library)
     target_compile_options(${library} PRIVATE "-Wdeprecated")
     target_compile_options(${library} PRIVATE "-Wshadow")
   endif()
+
+  if (FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+    target_compile_definitions(${library}
+      PRIVATE "FTXUI_MICROSOFT_TERMINAL_FALLBACK")
+  endif()
 endfunction()
 
 if (EMSCRIPTEN)
@@ -44,3 +49,4 @@ if (EMSCRIPTEN)
   string(APPEND CMAKE_CXX_FLAGS " -s USE_PTHREADS")
   string(APPEND CMAKE_CXX_FLAGS " -s PROXY_TO_PTHREAD")
 endif()
+

include/ftxui/component/checkbox.hpp

@@ -25,13 +25,8 @@ class CheckboxBase : public ComponentBase {
   CheckboxBase(ConstStringRef label, bool* state);
   ~CheckboxBase() override = default;
 
-#if defined(_WIN32)
-  std::wstring checked = L"[X] ";    /// Prefix for  a "checked" state.
-  std::wstring unchecked = L"[ ] ";  /// Prefix for  an "unchecked" state.
-#else
   std::wstring checked = L"▣ ";    /// Prefix for  a "checked" state.
   std::wstring unchecked = L"☐ ";  /// Prefix for  a "unchecked" state.
-#endif
 
   Decorator focused_style = inverted;   /// Decorator used when focused.
   Decorator unfocused_style = nothing;  /// Decorator used when unfocused.

include/ftxui/component/radiobox.hpp

@@ -27,13 +27,8 @@ class RadioboxBase : public ComponentBase {
 
   int focused = 0;
 
-#if defined(_WIN32)
-  std::wstring checked = L"(*) ";
-  std::wstring unchecked = L"( ) ";
-#else
   std::wstring checked = L"◉ ";
   std::wstring unchecked = L"○ ";
-#endif
 
   Decorator focused_style = inverted;
   Decorator unfocused_style = nothing;

include/ftxui/component/screen_interactive.hpp

@@ -56,8 +56,8 @@ class ScreenInteractive : public Screen {
 
   std::atomic<bool> quit_ = false;
 
-  int cursor_x_ = 0;
+  int cursor_x_ = 1;
-  int cursor_y_ = 0;
+  int cursor_y_ = 1;
 
   bool mouse_captured = false;
 };

src/ftxui/component/checkbox.cpp

@@ -40,7 +40,16 @@ CheckboxBase* CheckboxBase::From(Component component) {
 }
 
 CheckboxBase::CheckboxBase(ConstStringRef label, bool* state)
-    : label_(label), state_(state) {}
+    : label_(label), state_(state) {
+#if defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+  // Microsoft terminal do not use fonts able to render properly the default
+  // radiobox glyph.
+  if (checked == L"▣ ")
+    checked = L"[X]";
+  if (unchecked == L"☐ ")
+    unchecked = L"[ ]";
+#endif
+}
 
 Element CheckboxBase::Render() {
   bool is_focused = Focused();

src/ftxui/component/component_test.cpp

@@ -1,8 +1,8 @@
-#include <gtest/gtest.h>  // for Test, SuiteApiResolver, TestInfo (ptr only), TEST, TestFactoryImpl
 #include <memory>  // for shared_ptr, allocator, make_shared, __shared_ptr_access
 
 #include "ftxui/component/captured_mouse.hpp"  // for ftxui
 #include "ftxui/component/component_base.hpp"  // for ComponentBase, Component
+#include "gtest/gtest_pred_impl.h"  // for Test, SuiteApiResolver, TEST, TestFactoryImpl
 
 using namespace ftxui;
 

src/ftxui/component/radiobox.cpp

@@ -50,7 +50,16 @@ RadioboxBase* RadioboxBase::From(Component component) {
 
 RadioboxBase::RadioboxBase(const std::vector<std::wstring>* entries,
                            int* selected)
-    : entries_(entries), selected_(selected) {}
+    : entries_(entries), selected_(selected) {
+#if defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+  // Microsoft terminal do not use fonts able to render properly the default
+  // radiobox glyph.
+  if (checked == L"◉ ")
+    checked = L"(*)";
+  if (unchecked == L"○ ")
+    unchecked = L"( )";
+#endif
+}
 
 Element RadioboxBase::Render() {
   std::vector<Element> elements;

src/ftxui/component/screen_interactive.cpp

@@ -450,10 +450,25 @@ void ScreenInteractive::Draw(Component component) {
     cursor_.y = dimy_ - 1;
   }
 
-  static int i = -2;
+  // Periodically request the terminal emulator the frame position relative to
-  if (i % 10 == 0)
+  // the screen. This is useful for converting mouse position reported in
-    std::cout << DeviceStatusReport(DSRMode::kCursor);
+  // screen's coordinates to frame's coordinates.
+  static constexpr int cursor_refresh_rate =
+#if defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+      // Microsoft's terminal suffers from a [bug]. When reporting the cursor
+      // position, several output sequences are mixed together into garbage.
+      // This causes FTXUI user to see some "1;1;R" sequences into the Input
+      // component. See [issue]. Solution is to request cursor position less
+      // often. [bug]: https://github.com/microsoft/terminal/pull/7583 [issue]:
+      // https://github.com/ArthurSonzogni/FTXUI/issues/136
+      150;
+#else
+      20;
+#endif
+  static int i = -3;
   ++i;
+  if (!use_alternative_screen_ && (i % cursor_refresh_rate == 0))
+    std::cout << DeviceStatusReport(DSRMode::kCursor);
 
   Render(*this, document);
 

src/ftxui/dom/frame.cpp

@@ -53,7 +53,27 @@ class Focus : public Select {
 
   void Render(Screen& screen) override {
     Select::Render(screen);
+
+    // Setting the cursor to the right position allow folks using CJK (China,
+    // Japanese, Korean, ...) characters to see their [input method editor]
+    // displayed at the right location. See [issue].
+    //
+    // [input method editor]:
+    // https://en.wikipedia.org/wiki/Input_method
+    //
+    // [issue]:
+    // https://github.com/ArthurSonzogni/FTXUI/issues/2#issuecomment-505282355
+    //
+    // Unfortunately, Microsoft terminal do not handle properly hidding the
+    // cursor. Instead the character under the cursor is hidden, which is a big
+    // problem. As a result, we can't enable setting cursor to the right
+    // location. It will be displayed at the bottom right corner.
+    // See:
+    // https://github.com/microsoft/terminal/issues/1203
+    // https://github.com/microsoft/terminal/issues/3093
+#if !defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
     screen.SetCursor(Screen::Cursor{box_.x_min, box_.y_min});
+#endif
   }
 };
 

src/ftxui/dom/gauge.cpp

@@ -8,7 +8,13 @@
 
 namespace ftxui {
 
+#if defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+// Microsoft's terminals often use fonts not handling the 8 unicode characters
+// for representing the whole gauge. Fallback with less.
+static wchar_t charset[] = L"    ▌▌▌███";
+#else
 static wchar_t charset[] = L"  ▏▎▍▌▋▊▉█";
+#endif
 
 class Gauge : public Node {
  public:

src/ftxui/dom/graph.cpp

@@ -10,7 +10,13 @@
 
 namespace ftxui {
 
+// Microsoft's terminals often use fonts not handling the 8 unicode characters
+// for representing the whole gauge. Fallback with less.
+#if defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+const wchar_t charset[] = L"  █ █████";
+#else
 const wchar_t charset[] = L" ▗▐▖▄▟▌▙█";
+#endif
 
 class Graph : public Node {
  public:

src/ftxui/screen/terminal.cpp

@@ -23,12 +23,15 @@ Terminal::Dimensions Terminal::Size() {
   return Dimensions{140, 43};
 #elif defined(_WIN32)
   CONSOLE_SCREEN_BUFFER_INFO csbi;
-  int columns, rows;
 
-  GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi);
+  if (GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi)) {
-  columns = csbi.srWindow.Right - csbi.srWindow.Left + 1;
+    return Dimensions{csbi.srWindow.Right - csbi.srWindow.Left + 1,
-  rows = csbi.srWindow.Bottom - csbi.srWindow.Top + 1;
+                      csbi.srWindow.Bottom - csbi.srWindow.Top + 1};
-  return Dimensions{columns, rows};
+  }
+
+  // The Microsoft default "cmd" returns errors above.
+  return Dimensions{80, 80};
+
 #else
   winsize w;
   ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
@@ -61,6 +64,15 @@ Terminal::Color ComputeColorSupport() {
   if (Contains(COLORTERM, "256") || Contains(TERM, "256"))
     return Terminal::Color::Palette256;
 
+#if defined(FTXUI_MICROSOFT_TERMINAL_FALLBACK)
+  // Microsoft terminals do not properly declare themselve supporting true
+  // colors: https://github.com/microsoft/terminal/issues/1040
+  // As a fallback, assume microsoft terminal are the ones not setting those
+  // variables, and enable true colors.
+  if (TERM == "" && COLORTERM == "")
+    return Terminal::Color::TrueColor;
+#endif
+
   return Terminal::Color::Palette16;
 }